$ { \left[\begin{array}{rr}{-1} & {-1} \\ {0} & {0}\end{array}\right]+\left[\begin{array}{rr}{0} & {1} \\ {0} & {-2}\end{array}\right] = {?} } $
Explanation: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rr}{-1}+{0} & {-1}+{1} \\ {0}+{0} & {0}+{-2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{-1} & {0} \\ {0} & {-2}\end{array}\right]}$